Swordfish

Swordfish (Xiphias gladius)

Also known as: schwertfisch, broadbill, broadbill swordfish, broad-bill sword-fish, pez espada, emperador, espadon, shutome, dogso, agulha

Morphology & Biology

The swordfish is a large, fast and active predatory fish. They can reach swimming speeds of 70-100 km/h. Their name signifies their long, pointed bill, which can be up to a third of their total body length. The swordfish’s long bill is flattened and pointed, resembling the blade of a sword.

The maximum recorded size is 4.5m in length and 600kg in weight. Females are larger than males. Within the Mediterranean, swordfish do not tend to reach a large size: the average weight of individuals caught is between 115 to 160kg. However, in the western Atlantic swordfish are able to reach sizes of around 320kg, and out in the southeastern Pacific they can reach up to 530kg. 

They have a torpedo shaped body with strong fins. Their coloration ranges from black through dark gray to brown-red. Adult swordfish lose their teeth and scales. Adults have a high, pointed dorsal fin, and no ventral fin.

Distribution

The swordfish is a species widespread throughout the oceans, but prefers warmer waters. They can be found as far north as the North and Baltic Seas, though this is rare. They are more widely distributed in the Mediterranean, Atlantic and Pacific. They are a globally migratory species.

Swordfish are pelagic, living mostly in the open sea. Sometimes they will visit coastal waters, as they prefer temperatures between 18-22°C. In the northern hemisphere, these fish migrate in the winter to more southern areas, and deeper waters.

Threats

Swordfish in cuisine is very popular in Asia and the Mediterranean. As a result, swordfish is an economically important fish species that has been fished increasingly in recent years. As a consequence, populations are declining, according to the IUCN Red List and ICCAT.

Nowadays longlining is the main fishing method used to capture swordfish. This has led to increased capture rates. Longliners catch such large numbers of swordfish that there is concern that local populations may be fished to depletion in certain areas. Though there is a lack of evidence that swordfish populations have collapsed, assessments of fisheries have shown that fishing is being done at an unsustainable rate. For example, In the Indian Ocean, the population declined by 57.8% over 20 years. It is also important to remember that we only have the reported capture rates of fish – figures do not include illegal, unreported and unregulated fishing.

According to the IUCN Red List, swordfish has already experienced a worldwide decline of 28% over three generations (20 years). Despite this, swordfish are classified as a “least concern” species by the IUCN.

Fisheries & Aquaculture

^{Source: http://www.fao.org/fishery/species/2503/en}

The most common method of capturing swordfish is using longlines (a line several kilometers long, to which shorter side lines are attached, which in turn end with bait hooks). Harpoons and drift nets are also used. Harpoons and hand lines cause virtually no by-catch as they are highly selective, but are rarely used in commercial swordfish fisheries due to their low efficiency.

Longlining is the most popular choice of fishing equipment: in the Atlantic, most swordfish are caught in this way. Up to a third of the total catch of longlines will be bycatch (unwanted species that were not intended to be caught). This leads to the death or injury of many threatened or endangered species such as sharks, turtles and seabirds. Longlines are contributing to the extinction of these species. Currently, there are no international laws regulating bycatch.

The swordfish is a predator at the top of the food chain, playing an integral role in maintaining the ecosystem. If top predators such as the swordfish are depleted, other local marine wildlife could be thrown out of balance.

Fun fact

Swordfish have the ability to selectively increase the temperature of their eyes and brain, using heat exchange. They can heat up their eyes and brain to sharpen their perceptual acuity when hunting, and to compensate for temperature fluctuations in the water.